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Abstract
Hydroxyapatite (HA) based bioceramic coatings were deposited onto titanium alloy substrates
using the high velocity oxy-fuel (HVOF) spray technique. This study aimed to reveal
the relations among processing parameters, microstructure, and properties of the bioceramic
coatings. The processing conditions were altered through changing the starting HA
powder size, content of bioinert ceramic additives or composite powder preparation
techniques. Coating structure was characterized through scanning electron microscopy
(SEM) and transmission electron microscopy (TEM); and the mechanical properties, Young's
modulus and fracture toughness, of the coatings were evaluated through indentation
techniques. Results demonstrated dominant influence of the melt state of HA powders
on the phase composition of resultant coatings, and it was found that the HVOF HA
coatings possess competitive mechanical properties. Furthermore, addition of titania
or zirconia, as secondary phase in HA, showed promising effect on improving the mechanical
properties of the HVOF HA-based coatings. Chemical reactions between HA and titania;
and, HA and zirconia during coating deposition were revealed and characterized. Incorporation
modes of the additives into HA and their reinforcing mechanisms were elucidated. The
relationship among the processing, microstructure, and mechanical properties of the
HVOF sprayed bioceramic coatings was summarily examined.